r - Return row number(s) for a particular value in a column in a dataframe

Question

I have a data frame (df) and I was wondering how to return the row number(s) for a particular value (2585) in the 4th column (height_chad1) of the same data frame?

I've tried:

row(mydata_2$height_chad1, 2585)

and I get the following error:

Error in factor(.Internal(row(dim(x))), labels = labs) : 
  a matrix-like object is required as argument to 'row'

Is there an equivalent line of code that works for data frames instead of matrix-like objects?

Any help would be appreciated.

Answer 1

Use which(mydata_2$height_chad1 == 2585)

Short example

df <- data.frame(x = c(1,1,2,3,4,5,6,3),
                 y = c(5,4,6,7,8,3,2,4))
df
  x y
1 1 5
2 1 4
3 2 6
4 3 7
5 4 8
6 5 3
7 6 2
8 3 4

which(df$x == 3)
[1] 4 8

length(which(df$x == 3))
[1] 2

count(df, vars = "x")
  x freq
1 1    2
2 2    1
3 3    2
4 4    1
5 5    1
6 6    1

df[which(df$x == 3),]
  x y
4 3 7
8 3 4

As Matt Weller pointed out, you can use the length function. The count function in plyr can be used to return the count of each unique column value.